Marine waterjets have many benefits for propulsion of marine vessels, such as higher safety, higher efficiency, shallow draft and outstanding maneuverability. However, a disadvantage is the large amount of space taken up by the motor and the gearbox that are conventionally placed in front of the waterjet inside the vessel. The motor drives the waterjet by a transmission that adapts the rotational speed of the motor to that of the waterjet. A drive shaft with flexible couplings at each end, a shaft tube and a water seal connect the transmission to the impeller of the waterjet. The shaft and shaft tube pass through the waterjet intake duct, obstructing the water flow in the intake duct to the impeller, lowering the efficiency of the waterjet. U.S. Pat. No. 5,421,753 shows such a drive arrangement.
Waterjets are typically driven by internal combustion engines, which are both heavy and noisy. Also, in recent years, battery technology has developed rapidly, to the point where the stored energy densities of some batteries make electric propulsion of marine vessels a possibility. Further, advances in semiconductor switching technology enable numerous electric motor developments that would not have been possible in the past.